FIG. 3 shows a configuration of a conventional power supply apparatus. There is shown a power supply apparatus in which three power supply units 201 to 203 simultaneously supply power to a load 30.
There provided a circuit breaker 101 on an input side of the power supply unit 201. This circuit breaker 101 includes a switch 111 which connects/disconnects an input voltage Vac1 to the power supply unit 201. The power supply unit 201 converts the input voltage Vac1 to an output voltage V1 (see FIG. 4), and supplies the output voltage V1 to the load 30.
There provided a circuit breaker 102 on an input side of the power supply unit 202. This circuit breaker 102 includes a switch 112 which connects/disconnects an input voltage Vac2 to the power supply unit 202. The power supply unit 202 converts the input voltage Vac2 to an output voltage V2 (see FIG. 4), and supplies the output voltage V2 to the load 30.
There provided a circuit breaker 103 on an input side of the power supply unit 203. This circuit breaker 103 includes a switch 113 which connects/disconnects an input voltage Vac3 to the power supply unit 203. The power supply unit 203 converts the input voltage Vac3 to an output voltage V3 (see FIG. 4), and supplies the output voltage V3 to the load 30.
A power supply capacity of the load 30 is made equal to a total power supply capacity of the power supply units 201 to 203. Therefore, the power supply apparatus shown in FIG. 3 does not have a redundant configuration.
All of the switches 111 to 113 are in the off-state before the power supply is thrown in. When throwing in power supply, the switches are turned on in the order of the switch 111, the switch 112, and 113. If the switch 111 of the circuit breaker 101 is turned on at time t1 shown in FIG. 4, then the input voltage Vac1 is supplied to the power supply unit 201.
As a result, the output voltage V1 is supplied from the power supply unit 201 to the load 30. However, the power supply capacity of the load 30 cannot be satisfied with the output voltage V1 alone. Therefore, the output voltage V1 gradually droops as shown in FIG. 4.
If the switch 112 of the next circuit breaker 102 is turned on at time t2 shown in FIG. 4, then the input voltage Vac2 is supplied to the power supply unit 202. As a result, the output voltage V2 is also supplied from the power supply unit 202 to the load 30. At the time t2, the output voltage V1 also rises. In this instance, power is supplied from two power supply units 201 and 202 to the load 30.
However, the power supply capacity of the load 30 is not satisfied with the output voltages V1 and V2. As shown in FIG. 4, therefore, each of the output voltages V1 and V2 gradually droops from the time t2.
If the switch 113 of the next circuit breaker 103 is turned on at time t3 shown in FIG. 4, then the input voltage Vac3 is supplied to the power supply unit 203. As a result, the output voltage V3 is also supplied from the power supply unit 203 to the load 30. At the time t3, each of the output voltages V1 and V2 also rises.
In this instance, power is supplied from three power supply units 201, 202 and 203 to the load 30. Therefore, the power supply capacity of the load 30 is satisfied. As shown in FIG. 4, each of the output voltages V1, V2 and V3 becomes stable at a fixed value after the time t3.
As shown in FIG. 4, the conventional power supply apparatus has a problem that the rise and droop of the output voltages are repeated and the power supply to the load 30 becomes unstable until power of a power supply capacity required for the load 30 is supplied (i.e., between the time t1 and the time t3).
Lately when the power consumption of integrated circuits that form a part of the load 30 tends to increase, the number of the power supply units also increases to satisfy the required power supply capacity. As the number of power supply units increases, the time during which the power supply becomes unstable is prolonged. In the conventional power supply apparatus, therefore, the problem becomes remarkable.